FPGA时序约束和timequest timing analyzer

代码说明：

  约束所有时钟（包括你的设计中特有的时钟）对准确的时序分析结果而言是必不可少的。Quartus II TimeQuest Timing Analyzer为各种各样的时钟配置和典型时钟提供许多SDC命令。(Constraining all clocks, including the clocks unique to your design, is essential for accurate timing analysis results. The Quartus II TimeQuest Timing Analyzer provides many SDC commands for a variety of clock configurations and typical clocks.)